Do you have compensation guidelines (perhaps calculated as a percentage of an employees salary), for employees who take on additional responsibilities for set periods of time.  Ex: when you are actively recruiting for a role and you temporarily have a Leader take on an additional team and additional scope?

We dont have Compensation Guidelines for additional responsibilities however employees can take up additional projects (open projects within the organization that are listed), facilitating, content building etc for which they get reward points, which could be redeemed for merchandise from our catalogue. 

We grant an additional bonus amount (on top of the ordinary bonus/incentive) to compensate additional responsibility (eg: colleague covering maternity leave or open role while we manage recruitment). We prefer this in order not to: 1) alter compensation scheme according to job architecture; 2) avoid consolidation of this concept in payroll; 3) give specific "one time" value. 

We typically provide a spot bonus award after completion of the Acting Up opportunity depending on the length of time and complexity of the scope of work.  We don't base it exactly on their base pay, but use their base pay as an anchor.  We also speak to the learning that comes from taking on the additional responsibilities as part of the opportunity vs just a cash-oriented recognition.  This is largely our US practice, but we have leveraged this kind of concept in other regions.  We typically only give this kind of recognition if an individual has had these extended opportunities of 4+ months.  

Yes - we have guidance that use our salary bands to calculate Interim (full responsibility for short period) or Acting Up (part responsibility) allowances paid as a % of salary and not pension/benefit eligible.  These are for planned cover in advance where longer than 4 weeks (not rewarding if cover for someone on holiday for example) and most often using recruitment selection, but not always.